The present invention relates to systems and methods for providing electrical stimulation to bodily tissue, such as a portion of a patient's nervous system. More particularly, it relates to temporarily implantable electrical leads, such as a peripheral nerve evaluation lead used to stimulate a sacral nerve, that resist migration and, in some embodiments, are bipolar.
A number of human bodily functions are affected by the nervous system. For example, bodily disorders, such as urinary incontinence, urinary urge/frequency, urinary retention, pelvic pain, bowel dysfunction (constipation, diarrhea, etc.), erectile dysfunction, etc., are all bodily functions influenced by the sacral nerves. As a point of reference, urinary incontinence is the involuntary loss of control over the bladder. Incontinence is primarily treated through pharmaceuticals and surgery. Many pharmaceuticals do not adequately resolve the issue and can cause unwanted side effects; further, a number of surgical procedures have a low success rate and/or are not reversible. Similar treatment insufficiencies have likewise been noted for many of the other maladies previously mentioned.
As an alternative to conventional pharmaceuticals and/or invasive surgical procedures, neurostimulation has more recently been recognized as a viable treatment approach for many patients. By way of background, the organs involved in bladder, bowel, and sexual function receive much of their control via the second, third, and fourth sacral nerves, commonly referred to as S2, S3, and S4, respectively. Electrical stimulation of these various nerves has been found to offer some control over these functions. Several electrical stimulation techniques have been suggested, including stimulation of nerve bundles within the sacrum. Regardless, in order to consistently deliver electrical stimulation to the sacral nerve(s), certain anatomical obstacles must be addressed. The sacrum is a large, triangular bone situated at the lower part of the vertebral column, and at the upper and back part of the pelvic cavity. The spinal canal runs through the greater part of the sacrum. Further, the sacrum is perforated by the anterior and posterior sacral foramina though which the sacral nerves pass.
With the above anatomical description in mind, partial control over one or more of the functions (or dysfunctions) previously mentioned has been achieved by implanting a neurostimulation lead at or near the sacral nerves. As a point of reference, other nerve(s) or tissue can similarly be electrically stimulated to produce different effects. Relative to sacral nerve stimulation, however, the neurostimulation lead, having several stimulation electrodes, can be permanently implanted within and/or anteriorly beyond the sacral foramen at which the sacral nerve in question is anatomically located. Because the lead, and in particular the stimulation electrodes, must remain in operative proximity to the sacral nerve, the permanent lead (sometimes referred to as a “chronic lead”) can be sutured within the patient's body to resist migration. In light of the invasive nature associated with this approach, minimally invasive neurostimulation leads have been developed, incorporating features proximal the electrodes that inhibit migration and/or retrograde dislodgement. Permanent leads of this type are typically somewhat sizable to not only present a sufficient number of electrodes, but to also better resist migration. Regardless, wire cabling from the lead is implanted within a subcutaneously-formed tunnel and connected to a subcutaneously-implanted pulse generator. One example of such a system is available from Medtronic, Inc., of Minneapolis, Minnesota under the trade name InterStim®. Other chronic leads/systems are further described in U.S. Pat. Nos. 6,999,819; 6,971,393; and 6,847,849, each commonly assigned to the assignee of the present invention and the teachings of all of which are incorporated herein by reference.
Some patients may view the permanent neurostimulation lead and related pulse generator implantation described above as being a fairly traumatic procedure. Thus, efforts are conventionally made to ascertain in advance whether the patient in question is likely to receive benefit from sacral nerve stimulation. In general terms, the test stimulation procedure entails the temporary implantation of a neurostimulation lead in conjunction with an externally carried pulse generator or other power source. Once in place, the patient is exposed to neurostimulation over a trial period (e.g., 3-7 days) during which the patient can experience the sensation of nerve stimulation during various everyday activities, as well as record the changes, if any, in the bodily dysfunction of concern (e.g., a patient experiencing urinary incontinence can maintain a voiding diary to record voiding behavior and symptoms with the stimulation). The record of events is then compared with a base line and post-test stimulation diaries to determine the effect, if any, of sacral nerve stimulation on the symptoms being experienced by the patient. If the test stimulation is successful, the patient and his/her clinician can make a better informed decision as to whether permanent implantation and long-term sacral nerve stimulation is a viable therapy option.
Temporary implantation of the neurostimulation lead is normally done in one of two manners. With one approach, sometimes referred to as a “staged implantation,” a conventional, permanent or chronic neurostimulation lead is implanted at the desired sacral location, with the cable carrying the coiled conductor wiring being externally extended through the patient's skin and coupled to the pulse generator. While viable, this technique entails the use of surgical equipment normally employed to permanently implant the stimulation lead. By way of background, implantation of a permanent sacral nerve stimulation lead normally requires the use of a fairly large introducer (e.g., an elongated, 13 gauge tube), and the chronic stimulation lead has a fairly large diameter. While local and/or general anesthesia is available, some patients may be apprehensive to participate in a short-term test of this type in view of the size of the instrument(s)/stimulation lead.
To better address the reluctance of some patients to participate in the stimulation test procedure described above, a second technique has been developed that entails the use of a smaller diameter, more simplified neurostimulation lead intended to be implanted on only a temporary basis. In general terms, the temporary stimulation lead (sometimes referred to as a peripheral nerve evaluation lead or “PNE” lead) has a single electrode and is of sufficiently small diameter so as to be percutaneously inserted using a small diameter needle (e.g., a 20 gauge needle). Many patients are not overly threatened by a small diameter needle and thus are more likely to participate in the trial stimulation. The percutaneous test stimulation is similar to an epidural nerve block, except that the temporary lead is inserted and left in the patient's back during the trial. The end of the lead that remains on the outside of the patient's body is secured to the patient's skin with, for example, surgical tape. Upon conclusion of the trial stimulation, the lead is removed from the patient.
While generally preferred by patients, the percutaneous, PNE lead technique may have certain drawbacks. For example, while the temporary simulation lead is highly capable of delivering the necessary stimulation energy throughout the evaluation period, it is possible that the lead may migrate. For example, any pulling or tugging on the proximal end of the lead body (from outside of the patient's body) could be directly communicated to the lead's electrode, thus creating a higher likelihood of electrode dislodgement and poor stimulation. Efforts have been made to address this concern, for example as described in U.S. Pat. No. 6,104,960, the teachings of which are incorporated herein by reference and assigned to the assignee of the present invention. In particular, a temporary neurostimulation lead is described as having a coiled configuration that better accommodates axial forces placed onto the lead body (e.g., tugging or pulling on the proximal end of the lead body). Any additional efforts to further minimize migration of the temporary neurostimulation lead would be well received, not only in the one exemplary context of peripheral sacral nerve electrical stimulation, but also for any other procedure in which an implantable medical electrical stimulation lead is used. Further, conventional PNE-type leads incorporate only one electrode (i.e., a unipolar lead electrode), such that a return electrode (or ground pad) is typically applied to the patient's skin. The ground pad may cause the patient some discomfort, and in some instances can become dislodged or disconnected during the test period, thus preventing the test stimulation therapy from occurring.
In light of the above, a need exists for a medical electrical lead which may be safely and effectively implanted in a minimally invasive manner, but which better inhibits axial migration of dislodgement of the lead body from the stimulation site, such as a sacral location. Other needs exist for bipolar PNE-type leads.